PQQGDH is glucose dehydrogenase using pyrroloquinoline quinone as a coenzyme, and can be used for assay of blood glucose because it catalyzes a reaction in which glucose is oxidized to produce gluconolactone. A glucose concentration in blood is a very important indicator as an important marker for diabetes in clinical diagnosis. At present, the glucose concentration in blood is primarily measured by a biosensor using glucose oxidase, but some errors have been likely observed in measured values because the reaction is affected by a dissolved oxygen concentration. PQQ dependent glucose dehydrogenase has been noticed as a new enzyme in place of this glucose oxidase.
Our group has found that Acinetobacter baumannii NCIMB11517 strain produces PQQ dependent glucose dehydrogenase, cloned a gene thereof and constructed a high expression system thereof (see Patent document 1). PQQ dependent glucose dehydrogenase has had an issue with substrate specificity compared to glucose oxidase
[Patent document 1] JP HEI-11-243949 A Publication
When pyrroloquinoline quinone dependent glucose dehydrogenase is used for the biosensor, the ferricyanide ion is used as the mediator in a common blood glucose monitor. An enzyme is dissolved in blood of a specimen on its strip. The blood has higher viscosity and lower solubility than water and solvents used for other general reagents. Therefore, it is desirable that an amount of the enzyme to be added on the strip is small as the amount of a protein. Thus, it has been desired to acquire pyrroloquinoline quinone dependent glucose dehydrogenase which has an enhanced enzyme activity per unit protein, i.e., an enhanced specific activity.
There has been no report concerning modified pyrroloquinoline quinone dependent glucose dehydrogenase whose specific activity has been enhanced in the assay system using the ferricyanide ion as the mediator.